Increasingly, RF surgical generators are used for tissue cutting and coagulating. Compared with mechanical incisions, haemostasis of the cutting edges is considered one of the advantages of RF surgical incisions, this haemostasis being due to thermal coagulation, in particular. In this case, the depth of the coagulation zone is largely dependent on the perfusion of the treated tissue, resulting in the requirement that the depth of the coagulation zone used by the RF surgical generators can be adjusted in as reproducible a manner as possible. In conjunction with this, the shape of the RF output signals of the RF surgical generator is of importance and, in particular, the ratio of peak value to effective value. Consequently, amplitude-modified RF voltages (currents) are selected, where the modulation is sufficient for the RF surgical generator to potentially also generate only a single cycle followed by a longer pause.
Another requirement is that the RF surgical generator be as highly efficient as possible because, if the efficiency is too low, any heat loss must be removed by elaborate cooling measures, which is not desirable in the operating room.
German Publication DE 102 18 895 A1 discloses an RF surgical generator to achieve greater efficiency in that the DC voltage power supply usually provided for such RF surgical generators can work in two modes of operation, i.e., on one hand, it can work as a power supply for the power oscillator (in a conventional manner) and, on the other hand, it can work in a mode in which an energy transfer from the power supply of the power oscillator back to the input of the DC voltage power supply takes place. In this case, substantial improvements in shaping short pulses are not possible.
German Publication DE 100 46 592 A1 discloses an RF surgical generator of the type addressed herein. In this generator, the ohmic resistance is withdrawn when the RF output signal is to be completed, said ohmic resistance being connected parallel to the consumer, as it were. The efficiency of this device, however, is minimal.